Stabilized lubricants



United States This invention relates to improved lubricants. More particularly, it relates to lubricants possessing outstanding resistance against oxidative deterioration.

Industrial and engine lubricantse.g., mineral oils and synthetic diester oilsundergo oxidative deterioration in service, panticularly at elevated temperatures. Resulting from this deterioration are the formation of gums and sludges, the-corrosion of metal parts of the equipment with which the oils are used, the loss of'lubricating properties of the oil, and the like. Shortcomings of prior antioxidants include low effectiveness except at high concentration, low solubility in the oil, high cost, and difficulty of preparation. Furthermore, most prior art antioxidants'possess marginal effectiveness whenthe oils are subjected to drastic oxidizing conditions, such as are encountered when the oils' are held at elevated temperatures, agitated'with air, and contain in suspension iron and other metal oxides which catalyze the decomposition of the oil.

An object of this invention is to provide lubricants characterized by greatly enhanced resistance to oxidative deterioration, particularly at elevated temperatures. Another object is to provide' additives which markedly enhance the resistance of engine and industrial oils against oxidative deterioration, especially under the foregoing drastic conditions. A'further' object is to provide synergistic combinations of additives which very-effectively inhibitthe oxidative deterioration of lubricating oil. Other important objects will be apparent as the description proceeds.

These and other objects are accomplished by this invention'which consists of providing lubricating oil normally susceptible to oxidative deterioration containing a small antioxidant quantity of a synergistic mixture consisting of fromabout 0.001 to about0.2- and preferably 0.03 to O.1-per'cent by weight based on the oil of phosphorus as a dialkyl hydrogen phosphite in which the alkyl groups each contain up to about '12 carbon atoms, and from about 0.01 to about 3preferably 0.05 to 1-percentby weight based on the oil'of an ortho-alkyl phenol i aving theformula:

R3 wherein R is isopropylor tert-butyl, and R and R are selected from the group consisting of hydrogen and alkyl groups containing up to 3 carbon atoms, at least one of R and R being hydrogen and the total number of carbon atoms in R and R not exceeding six.

Such lubricants possess unexpectedly great resistance against oxidative deterioration, this resistance resulting from the presence therei'n'of the specified combination of additives which'co-act synergistically. The magnitude of the synergism is tremendous. For example, it has been found by actual tests that lubricants containing the above synergistic additives have their useful lives prolonged by well over 1000 times. This is especially striking since none of the above additives when used alone even begins to approximate such effectiveness.

These unexpected and disproportionately increased atet ice

anti-oxidant effects of this invention show up under all normal conditions encountered in the manufacture, slhipment, storage and useof lubricants. Itis especially significant that the synergism is very pronounced under high temperature oxidizing conditions since there is a real need for lubricants that are stable under these conditions. Moreover, these synergistic effects are undaunted by the presence in the oil of deleterious oxidation catalysts,'such as iron oxide, which at high temperatures normally promote' catastrophic deterioration of lubricants.

The invention is particularly applicable to lubricants which normally tend to deteriorate at elevated temperatures below the cracking temperature of the oil. Hence, the present synergistic additive combinations are eminently effective in mineral oils and synthetic \diester oils. Typical of the latter are diester oils of, the type described in Industrial and Engineering Chemistry, 39, 484-91 (1947). In general, these diester lubricants have molecular weights from about 300'to about 600 and freezing points and pour points ranging from about 40 to less than F. They include oxalates, malon'ates, succinates, glutara tes, adipates, pimelates, suberates azelates, sebacates, etc., especially thealkyl and cycloalkyl esters. Esters formed'from polyol-s (pentaerythritrol, trimethylol propane, etc.) and aliphatic monocarboxylic acids '(e.g., fatty acids) are also greatly improved instability by these additive combinations.

The dialkyl hydrogen phosphites used in this invention are those in which the alkyl groups each contain up to about 12 carbon atoms. Typical of these are dimethyl hydrogen phosp'hite, diisopropyl hydrogen phosphite, disec-butyl hydrogen phosphite, bis-(2-ethy lhexyl) hydrogen phosphite, dido'decyl hydrogen phosphite, ethyl isoheptyl hydrogen phosphite, and the like. On the basis of cost-effectiveness and ease of manufacture, those made from primary or secondary alcohols of 1 to 8 carbons are preferred. When used alone, rail of these phosphites are reasonably effective antioxidants under mildly oxidizing conditions. However, their effectiveness falls off sharply at elevated temperatures, especially in the presence of iron oxides. It is thus remarkable that when these materials are combined with the particular alkyl phenolsdescribed herein, such powerful synergistic effects are achieved even under these drastic conditions. U

The alkyl phenols used in this invention are certain mono-or dialkyl phenols-i.e., certain mono-ortho-alkyl phenols and specific 2,4- and 2,6-dialkyl phenols. The structure of these compounds is very important. The exceedingly valuable synergistic effects of this invention definitely appear to be tied in, in some unexplainable manner, with the configuration, chain length and relative positions of the alkyl groups. This is borne out by tests showing that departures from the above specific structural criteria of the alkyl phenol ingredient result not only in loss of synergistic effect, but in a very sharp drop in over-all effectiveness even when such other phenolic compounds are used with dialkyljhydrogen phosphites. It is especially noteworthy that decidedly inferior results have been achieved by combining 4-methyl- 2, 6-di-tert-butyl phenol with dialkyl hydrogen phosphites. Why this should be the case is a question which presently cannot be answered especially since 4methyl-2,6-di-t'ertbutyl phenol is a standard, commercially-used and gerierally effective antioxidant. Thus, coupled with the complete unexpectedness of the synergistic effects of this invention is the further unexpected contribution of the chemical structure of the alkyl phenol ingredient.

Examples of the alkyl phenol ingredient of the lubricants of this invention are 2-isopropyl phenol; 2-ethyl-6- isopropyl phenol; 2-isopropyl-4-methyl phenol; 2,4- diisopropyl phenol: 2-ethyl-6-tert-butylphenol; 2-tert-butyl-4- butyl phenol; 2,6-diisopropyl phenol; 2-methyl-6-tert-butyl,

phenol; and 2-tert-butyl-4-methyl phenol, since they give exceedingly large synergistic. effects with 2-methyl-6-tertbutyl'phenol and 2-tert-butyl-4-methyl phenol being outstanding in this regard.

Synergistic efiects are exhibited when the above combinations of additives are present in the lubricant in the concentration ranges described above. However, it has been further found that the greatest amount of synergism occurs when the dialkyl hydrogen phosphite and alkyl phenol are present in certain relative proportions within the range of the foregoing concentrations. Thus, a particularly preferred embodiment of this invention consists in providing lubricant compositions as described above further characterized in that the dialkyl hydrogen phosphite and alkyl phenol are present in relative proportions such that there are from about 0.5 to about 5 molecular equivalents of the phosphite per equivalent of alkyl phenol. V In formulating the lubricants, the above synergistic additives are blended in appropriate quantity with the oil, the phosphite and the phenol being used either as a preformed blend or mixture, or by adding them separately in either order.

The following examples illustrates various specific embodiments of this invention. Parts and percentages are by weight. The physical characteristics of the illustrative oils used in Examples 1 through 9 are shown in Table I.

TABLE I.PROPERTIES OF REPRESENTATIVE PETROLEUM HYDROCARBON OILS Oil A B O I D l E i F Gravity at 60 API 30.3 30. 5 28.8 31.1 20. 5 31.0 Viscosity, Saybolt;

Seconds at 100 F..- 178. 8 373. 8 309. 8 169. 249. 4 335. 4

Seconds at 210 F-.-" 52.0 58. 4 63. 8 51. 5 45. 7 68. 4 Viscosity Index 154. 2 107. 4 141. 9 157. 8 35. 8 144. 4 Pour Point 1. 30 +10 -20 0 Flash Point 410 465 365 385 Sulfur, percent 0.2 0.3 0. 3 0. 3 0.3 0. 1

Example 1 To 100,000 parts of oil A is added with stirring 5.3 parts of (0.001 percent of phosphorus as) diisopropyl hydrogen phosphite. To this oil is then added 1000 parts (1 percent) of 2-isopropyl phenol. The resultant oil possesses greatly enhanced resistance to oxidative deterioration. 7

Example 2 To 100,000 parts of oil B are added 1250 parts of (0.2 percent of phosphorus as) dibutyl hydrogen phosphite and 50 parts (0.05 percent) of 2-isopropyl-4-ethyl phenol. After mixing, the resulting oil possesses greatly enhanced oxidation resistance.

Example 3 With 100,000 parts of oil C are blended 490 parts of (0.05 percent of phosphorus as) dioctyl hydrogen phosphite and 10 parts (001 percent) of 2-propyl-6-isopropyl' phenol. The resulting oil is found to possess markedly great resistance to oxidative deterioration.

Example 4 To 100,000 parts of oil D are added 1160 parts of (0.1 percent of phosphorus as) di-(decyl) hydrogen phosphite and 500 parts (0.5 percent) of 2-ethyl-6-tert-butyl phenol. After agitation, the homogeneous lubricant possesses especially great resistance against oxidative deterioration.

Example 5 With 100,000 parts of oil E are blended 31 parts of (0.005 percent of phosphorus as) diisobutyl hydrogen phosphite and 100 parts (0.1 percent) of 2-tert-butyl-4- isopropyl phenol. Thev resu an l ricant i fOllnd to a viscosity at 210 Lis added 800 parts possess great resistance to high temperature oxidative deterioration.

Example 6 To 100,000 parts of oil F are added 540 parts of (0.15 percent of phosphorus as) dimethyl hydrogen phosphite and 3000 parts (3 percent) of 2-tert-butyl-4-ethyl phenol. After mixing, the resultant oil is greatly resistant to oxidative deterioration.

Example 7 With 100,000 parts of oil A are blended 93 parts of (0.08 percent of phosphorus as) bis-(2-dodecyl) hydrogen phosphite and 20 parts (0.02 percent) of 2,6-diisopropyl phenol. Greatly increased is the resistance of this oil against oxidative deterioration.

Example 8 To 100,000 parts of oil B are added 1 6.8 parts of (0.002 percent of phosphorus as) butyl-undecyl hydrogen phosphite and 500 parts (0.5 percent) of 2-methyl-6- isopropyl phenol. The finished oil is very highly resistant to oxidative deterioration.

Example 9 To 100,000 parts of a commercially-available pentaerythritol ester having a viscosity at F. of 22.4 centistokes and known in the trade as Hercofiex 600 are added 726 parts of (0.09 percent of phosphorus as) bis- (4-methyl-2-pentyl) hydrogen phosphite and 10 parts (0.01 percent) of 2-metl1yl-6-tert-butyl phenol. The resultant finished oil possesses markedly improved resistance against oxidative deterioration.

Example 11 With 100,000 parts of di(sec-amyl) sebacate having a viscosity at 210 F. of 33.8 Saybolt Universal seconds (SUS), a viscosity index of 133 and a molecular weight of 342.5 are blended 312 parts of (0.05 percent of phosphorus as) di-sec-butyl hydrogen phosphite and 300 parts (0.3 percent) of 2-tert-butyl phenol. The resistance to oxidative deterioration of the resultant oil is greatly improved.

Example I2v To 100,000 parts of di-(Z-ethylhexyl) sebacate having F. of 37.3 SUS, a viscosity index of 152 and a molecular weight of 426.7 are added parts of (0.05 percent of phosphorus as) dimethyl hydrogen phosphite and 546 parts of (0.05 percent of phosphorus as) bis-(2,6-dirnethylheptyl) hydrogen phosphite. Next (0.8 percent) of 2-tert-butyl-4-methyl phenol. The resultant homogeneous lubricant has extremely great resistance against oxidative deterioration.

Example I 3 To 100,000 parts of di-(Z-ethylhexyl) adipate having F. of 34.2 SUS, a viscosity index of 121 and a molecular weight of 370.6 are added 1120 parts of (0.18 percent of phosphorus as) di-tert-butyl hydrogen phosphite and 2000 parts (2 percent) of 2-isopropyl-4- propyl phenol. After mixing, the resultant diester lubricant is very resistant to oxidative deterioration.

Example 14 With 100,000 parts of di-sec-amyl) sebacate having a viscosity at 210 F. of 33.8 SUS, a viscosity index of 133 and a molecular weight of 342.5 are blended 8.9 parts of (0.002 percent of phosphorus as) bis-(2-nonyl) hydrogen phosphite, 500 parts (0.5 percent) of Z-methylfi-tert-butyl phenol and 200 parts (0.2 percent) of 2-tertbutyl-4-methyl phenol. The mixture is agitated and the resultant homogeneous lubricant has very high resistance to oxidative deterioration.

Example 15 To 100,000 parts of dioctyl sebacate having a viscosity at 210 F. of 36.7 SUS, a viscosity index of 159 and a molecular weight of 426.7 are added 106 parts of (0.02 percent of phosphorus as) dipropyl hydrogen phosphite and 40 parts (0.04 percent) of 2,6-diisopropyl phenol. The mixture is agitated to insure homogeneity. The finished oil is greatly resistant to oxidative deterioration.

In all of the foregoing illustrative examples, the increased resistance to oxidative deterioration results from a very substantial synergistic co-action of the additive combinations containing the preferred alkyl phenols, namely, 2,6-diisopropyl phenol, Z-tert-butyl phenol, and especially 2-methyl-6-tert-butyl phenol and 2-tert-butyl-4- methyl phenol, or mixtures thereof.

To illustrate the striking benefits of this invention a standard oil oxidation test was used. The equipment and test procedure as described by Kroger et al., Erdol and Kohle, 2, 389 (1949), served as the basis of the following tests. The equipment and procedure were slightly modified in order to make the oxidizing conditions even more strenuous. In this manner, the test lubricants were subjected to exceedingly severe oxidizing conditions in order to conclusively establish the elfectiveness of the additives under very adverse conditions. Furthermore, the modifications were found to provide results which correlated extremely well with test results of other standard procedures, including actual engine tests.

The equipment consists of a reaction cell connected with an open end manometer whereby the total uptake of oxygen by the oil can be obtained by noting the drop in mercury in the manometer. Thus, the test oil sample is placed in the reaction cell which is flushed with oxygen and the temperature raised to 300 F. and held there until the substrate oil undergoes catastrophic oxidation as shown by the rapid uptake of oxygen. In all cases, the substrate oil was deliberately contaminated with iron hexoate as an oxidation promotor (0.05 weight percent of iron as Fe O per 100 grams of oil). By so doing, a very close simulation of stringent oxidizing conditions prevailing with many uses of lubricants was achieved.

In the following tests, the oxidation stability of the test lubricant was determined by measuring its induction period, that is, the time required for catastrophic deterioration to occur under the foregoing conditions.

Hence, the longer the induction time, the more stable was the lubricant.

In one series of tests, the base lubricant was a commercially-available, additive-free mineral oil having a viscosity of 87.1 SUS at 100 F. and a viscosity index of 106.5. It was found that the presence of 0.03 percent by weight of phosphorus as dimethyl hydrogen phosphite gave an induction time of only three minutes. When 2-methyl-6-tert-butyl phenol was the sole additive (0.2 percent by weight), the induction time was twelve minutes. However, when the base oil contained 0.03 percent by weight of phosphorus as dimethyl hydrogen phosphite and 0.2 percent by weight of 2-methyl-6-tert-butyl phenol, the induction time was a phenomenal 1194 minutes.

In another example, the presence in the base oil of 0.19 percent by weight of 2-tert-butyl-4-methyl phenol and 0.04 percent by weight of phosphorus as dimethyl hydrogen phosphite gave the amazing induction time of 1498 minutes. In contrast to this, neither of the additives when used alone at these concentrations even caused the induction time to be lengthened by 20 minutes.

In still another example, the combination of 2-tertbutyl phenol (0.2 percent by weight) and dimethyl hydrogen phosphite (0.03 percent by weight of phosphorus) gave an induction time of 911 minutes. The enormous synergistic effect is clear from the fact that separately, 0.2 percent by weight of Z-tert-butyl phenol gave an induction time of 33 minutes and 0.03 percent by weight of phosphorus as dimethyl hydrogen phosphite gave only 3 minutes.

The presence in the mineral oil of 0.19 percent by weight of 2,6-diisopropyl phenol and 0.045 percent by weight of phosphorus as dimethyl hydrogen phosphite likewise gave an exponentially-lengthened induction time. The actual value was 810 minutes as compared with the infinitesimally small times provided by each of the additives when used separately.

The great importance of the structure of the phenol used in this invention is clearly shown by the following comparative tests. Individual blends using the above base oil were made up as follows: Phenol (0.11 percent) plus 0.04 percent of phosphorus; meta-cresol (0.12 percent) plus 0.03 percent of phosphorus; 2,4,6-tri-tert-butyl phenol (0.32 percent) plus 0.03 percent of phosphorus; and 4-methyl-2,6-di-tert-butyl phenol (0.23 percent) plus 0.04 percent of phosphorus; in each case the phosphorus being present as dimethyl hydrogen phosphite. With these blends, the induction times were all very small. The phenol-phosphite combination lasted 19 minutes, the meta-cresol combination survived for 22 minutes, the 2,4,6-tri-tert-butyl phenol combination held up for 15 minutes, and the 4-methyl-2,-di-tert-butyl phenol mixture managed to reach 118 minutes. Obviously, these values are infinitesimally small as compared with the phenomenal results characterizing this invention. Furthermore, not only are the compositions of this invention different in kind from somewhat similar compositions not of this invention, but the present invention is of considerable economic importance. The alkyl phenols used in this invention are easily made from readily available and inexpensive starting materials. They are considerably less expensive than the comercially used 4-methyl- 2,6-di-tert-butyl phenol which is a high cost, fine chemi-. cal.

The benefits of this invention are still further demonstrated by carrying out engine tests, such as CRC L-38 test, as described in Development of Research Technique for Study of the Oxidation Characteristics of Crankcase Oils in the CLR Oil Test Engine, published by the Coordinating Research Council, New York, March 1957. This test very effectively evaluate the oxidation and copper-lead bearing corrosion characteristics of engine crankcase oils. The technique involves operating the CLR oil test engine under constant speed, air/ fuel ratio, and fuelflow conditions for a total of 40 hours, subsequent to a break-in period of 4.5 hours. Prior to each test, the engine is cleaned, pertinent measurements of engine parts are taken and a complete set of new piston rings and new copper-lead connecting-rod test bearing inserts are installed. The chief operating conditions are:

Speed 3150: 25 rpm. Fuel-flow 4.5 to 5.0 lb./hr. Air/fuel ratio 140:0.5. Intake-air temperature F., min. Jacket-outlet coolant temperature 200- *-2- F.

Spark advance 35il BTDC. Oil pressure 40:2 p.s.i. Crankcase vacuum 21-05 in. water. Exhaust back pressure 0 to 1 in. mercury.

Performance of the oil is judged by visual examination of the engine for deposits, by the weight loss of the test bearing and by comparison of inspection data on used oil samples with the inspection data on the new oil. When a typical additive-free, lubricating oil, such as any of those described in Table I, is subjected to this test, it is found that there has been a substantial weight loss of the test bearings and a considerable amount of deterioration of the oil. However, repetition of the test with the sole variable being that the oil is treated with an appropriate concentration of mixtures of dialkyl hydrogen phosphites and alkyl phenols of this invention shows that on completion of the test, there has been a substantial reduction in the weight loss of the test bearings and that the used oil has been virtually unaffected.

Preparation of the phosphites is described in Industrial and Engineering Chemistry, 49, 1871 (1957), and the alkyl phenols in co-pending application, Serial No. 426,556, filed April 29, 1954, now Patent No. 2,831,898.

The additives of this invention very elfectively stabilize such lubricating and industrial oils as crankcase lubricating oils, transformer oils, turbine oils, transmission fluids,

heptyl) pimelate; di-(3-decyl) suberate; di-sec-amyl g1u' tarate; di-(isobutyl) glutarate; di-(2-ethylbutyl) glutarate; di-(Z-ethylhexyl) glutarate; di-sec-amyl adipate, di-(3- methylbutyl) adipate; diethyl adipate; di-(4-propylcyclohexyl) adipate; di-2-ethylhexyl adipate; di-sec-amyl azelate; di-(isobutyl) azelate; di-(Z-ethylbutyl) azelate; di-(Z-ethylhexyl) azelate; di-sec-amyl sebacate; di-secbutyl sebacate; di-(Z-ethylhexyl) sebacate; bis-(l-methyll-cyclohexyl) sebacate; the glutarates, adipates, azelates and sebacates of branched chain secondary alcohols, such as undecanol, tetradecanol; etc.; the butyl pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, and dodecyl esters of polyols, such as pentaerythritol, trimethylol propane, trimethylol ethane, etc.; and, in general, esters of the type described in the literature as useful for synthetic lubricant purposes.

In the compositions of this invention effective use can be made of other additives which are known to the art, such as other inhibitors, detergent-dispersants, pour point depressants, viscosity index improvers, anti-foam agents, rust inhibitors, oiliness or film strength agents, dyes, and the like. Of the inhibitors which can be ef fectively used with the present additive combinations are sulfurized sperm oil, sulfurized terpenes, sulturized paraffin wax olefins, aromatic sulfides, alkyl phenol sulfides, lecithin, neutralized dithiosphophates, phosphorus pentasulfide-terpene reaction products, diphenylamine, phenylnaphthyl amine, and the like. Typical of the detergent additives that can be used in the compositions of this in vention are metallic soaps of high molecular weight acids, such as aluminum naphthenates, calcium phenyl stearates, calcium alkyl salicylates, alkaline earth metal petroleum sulfonates, alkaline earth metal alkyl phenol sulfides (barium amyl phenol sulfide, calcium octyl phenol disulfide, etc.), metal salts of wax-substituted phenol derivatives, and the like. Of the viscosity index improvers and pour point depressants, elfective use can be made of polymers of the esters of methacrylic acids and higher fatty alcohols and the corresponding polymeric esters of acrylic acid and higher fatty alcohols. These and other additives which can be employed in the compositions of this invention will now be Well known to those skilled in the art. 1

The following tests further demonstrate the synergism exhibited by particular phosphite-phenol combination antioxidants of this invention in both petroleum hydrocarbon derived and synthetic lubricating oil.

The equipment and test procedure was that described a in the tests set forth following Example 15. In this manner, the test lubricants were subjected to exceedingly severeoxidizing conditions in order to conclusively estabconditions.

The oxidation stability of the test lubricant was determined by measuring its induction period, that is, the

.time required for catastrophic deterioration to occur under the foregoing conditions. Hence, the longer the induction time, the more stable was the lubricant.

In one series of tests, the base lubricant was a commercially available additive-free highly refined mineral oil having a viscosity of 87.1 SUS at F. and a viscosity index of 106.5. In order to establish a base line for the tests, the oil was tested without adding antioxidant but with the above described iron hexaoate catalyst. In addition to the base line test, tests were conducted with individual phenols and phosphorus esters alone and in combination. The results of these tests are shown in Table II.

TABLE II Cone. of Cone. of phenolic phosphite Induction Additive (wgt. per- (wgt. perme cent) cent phos- (minutes) phorus) None 0 0 3 Dimethyl hydrogen ph0sphite 0 0.037 3 D0 0 0. 068 3 2-Tcrt-butylphenol 0. 37:6 0 212 2-Mcthyl-G-tert-butylphenol. 0. 386 0 214 2,6-Dlis0propy1phenol 0.21 0 77 D0 0. 427 O 141 2-Tert-butyl-l-methylphen0l O. 386 0 227 Dirnethyl hydrogen phosphite plus 2-tert-butylphe11ol 0.199 0.032 810 2-Methyl-6-tert-butylphenol plus dimethy] hydrogen phosphite- 0. 096 O. 019 89 The data in Table II show that action takes place between the phosphite and phenols tested. in each case the total expected antioxidant activity of the phenol and phosphite combination is less than that atcually achieved, and in addition, the activity achieved by the mixture cannot be obtained by doubling the concentration of either the phosphite or phenol.

In addition to the above tests in a mineral lubricating oil, tests were also conducted on a synthetic diester lubricant. The test procedure and equipment was the same as described above. The oil employed was a di(2-ethylhexyl) sebacate having a Saybolt viscosity at 100 F. of 68.3, a Saybolt viscosity at 210 F. of 37.3, and a viscosity index of 150.

The results of these tests are shown in Table III.

a definite synergistic These data show that the phosphite used had practically no efiect on the induction period of the oil and that using approximately one-half of the concentration of each of the phosphite and para-cresol, the effectiveness was over four times that obtained with 2-methyl-6-tertbutylphenol alone at twice the concentration.

Thus, the above tests demonstrate that a definite synergism is exhibited by the phenol and phosphite combinations of this invention and that this synergism is'applicable to synthetic lubricants as well as lubricants derived from refined petroleum products.

This application is a continuation-in-part of application Serial No. 713,297, filed February 5, 1958, and now abandoned, entitled Stabilized Lubricants.

We claim:

1. A lubricating oil selected from the group consisting of petroleum hydrocarbon oils and synthetic diester oils normally susceptible'to oxidative deteriorationcontaining a small antioxidant quantity of a synergistic mixture consisting of from about 0.001 to about 0.2 percent by weight based on the oil of phosphorus as a dialkyl hydrogen phosphite in which the alkyl groups each contain up to about 12 carbon atoms and from about 0.01 to about 3 percent by weight based on the oil of an ortho-alkyl phenol having the formula wherein R is selected from the group consisting of isopropyl and tert-butyl and R and R are selected from the group consisting of hydrogen and alkyl groups containing u to 3 carbon atoms, at least one of R and R being hydrogen and the total number of carbon atoms in R and R not exceeding six.

2. Petroleum hydrocarbon lubricating oil normally susceptible to oxidative deterioration containing a small antioxidant quantity of a synergistic mixture consisting of from about 0.001 to about 0.2 percent by weight, based on the oil, of phosphorus as dialkyl hydrogen phosphite in which the alkyl groups each contain up to about 12 carbon atoms and from about 0.01 to about 3 percent by weight, based on the oil, of an ortho alkylphenol selected from the group consisting of Z-tert-butylphenol, 2- methyl-6-tert-butylphenol, 2 tert-butyl-4-methylphenol and 2,6-diisopropylphenol.

3. Petroleum hydrocarbon lubricating oil normally susceptible to oxidative deterioration containing a small antioxidant quantity of a synergistic mixture consisting of from about 0.001 to about 0.2 percent by weight, based on the oil, of phosphorus as dimethyl hydrogen phosphite and from about 0.01 to about 3 percent by weight, based on the oil, of an ortho alkylphenol selected from the group consisting of Z-tert-butylphenol, 2-methyl-6-tertbutylphenol, 2-tert-butyl-4 methylphenol and 2,6-diisopropylphenol.

4. Petroleum hydrocarbon lubricating oil normally susceptible to oxidative deterioration containing a small antioxidant quantity of a synergistic mixture consisting of from about 0.001 to about 0.2 percent by weight, based on the oil, of phosphorus as dimethyl hydrogen phosphite and from about 0.01 to about 3 percent by weight, based on the oil, of an ortho alkylphenol having the formula is wherein R is selected from the group consisting of isopropyl and tert-butyl and R and R are selected from the group consisting of hydrogen and alkyl groups containing up to 3 carbon atoms, at least one of R and R being hydrogen and the total number of carbon atoms in R and R not exceeding six.

5. Petroleum hydrocarbon lubricating oil normally susceptible to oxidative deterioration containing a small antioxidant quantity of a synergistic mixture consisting of from about 0.001 to about 0.2 percent by weight, based on the oil, of phosphorus as dimethyl hydrogen phosphite and from about 0.01 to about 3 percent by weight, based on the oil, of Z-tert-butyl-4-methylphenol.

6. Petroleum hydrocarbon lubricating oil normally susceptible to oxidative deterioration containing a small antioxidant quantity of a synergistic mixture consisting of from about 0.001 to about 0.2 percent by weight, based on the oil, of phosphorus as dimethyl hydrogen phosphite and from about 0.01 to about 3 percent by weight based on the oil, of 2-methyl-6-tert-butylphenol.

7. Petroleum hydrocarbon lubricating oil normally susceptible to oxidative deterioration containing a small antioxidant quantity of a synergistic mixture consisting of from about 0.001 to about 0.2 percent by weight, based on the oil, of phosphorus as dimethyl hydrogen phosphite and from about 0.01 to about 3 percent by weight, based on the oil, of Z-tert-butylphenol.

8. Petroleum hydrocarbon lubricating oil normally susceptible to oxidative deterioration containing a small antioxidant quantity of a synergistic mixture consisting of from about 0.001 to about 0.2 percent by weight, based on the oil, of phosphorus as dimethyl hydrogen phosphite and from about 0.01 to about 3 percent by weight, based on the oil, of 2,6-diisopropylphenol.

9. Synthetic diester lubricating oil normally susceptible to oxidative deterioration containing a small antioxidant quantity of a synergistic mixture consisting of from about 0.01 to about 0.2 percent by weight, based on the oil, of di-sec-butyl hydrogen phosphite and from about 0.01 to about 3 percent by weight, based on oil, of a substituted phenolic compound having the formula Rr- -Rz wherein R is selected from the group consisting of iso propyl and tert-butyl and R and R are selected from the group consisting of hydrogen and alkyl groups con taining up to 3 carbon atoms, at least one of R and R being hydrogen and the total number of carbon atoms in R and R not exceeding six.

10. Synthetic diester lubricating oil normally susceptible to oxidative deterioration containing a small antioxidant quantity of a synergistic mixture consisting of from about 0.01 to about 0.2 percent by weight, based on the oil, of di-sec-butyl hydrogen phosphite and from about 0.01 to about 3 percent by weight, based on the oil, of Z-methyl--tert-butylphenol.

11. A di-(2-ethyl-hexyl) sebacate synthetic diester lubricating oil normally susceptible to oxidative deterioration containing a small antioxidant quantity of a synergistic mixture consisting of from about 0.01 to about 0.2 percent by weight, based on the oil, of di-sec-butyl hydrogen phosphite and from about 0.01 to about 3 percent by weight, based on the oil, of 2-methyl-6-tert-butylphenol.

12. A lubricating oil selected from the group consisting of mineral oils and synthetic diester oils normally susceptible to oxidative deterioration containing a small antioxidant quantity of a synergistic mixture consisting of from about 0.001 to about 0.2 percent by weight, based on the oil, of phosphorus as a dialkyl hydrogen phosphite selected from the group consisting of dimethyl hydrogen phosphite and di-sec-butyl hydrogen phosphite and from 0.01 to about 3 percent by weight, based on the oil, of an ortho alkyl phenol selected from the group consisting of Z-tert-butylphenol, 2-methyl-6-tert-butylphenol, 2-tertbutyl-4-methylphenol and 2,6-diisopropylphenol.

13. Mineral oil normally susceptible to oxidative deterioration containing a small antioxidant quantity of a synergistic mixture consisting of from about 0.001 to about 0.2 percent by weight, based on the oil, of phosphorus as a dialkyl hydrogen phosphite selected from the group consisting of dimethyl hydrogen phosphite and di-sec-butyl hydrogen phosphite and from 0.01 to about 3 percent by weight based on the oil of an ortho alkyl Z-tert-butylphenol, Z-methyl-6-tert-butylphenol, 2-tertbutyl-4-methylphenol and 2,6-diisopropylphenol.

References Cited in the file of this patent UNITED STATES PATENTS 2,101,632 Weinrich Dec. 7, 1937 2,169,185 Shoemaker et a1. Aug. 8, 1939 2,202,877 Stevens June 4, 1940 2,220,851 Schreiber Nov. 5, 1940 2,413,353 Hunter et a1 Dec. 31, 1946 2,726,226 Werkheiser Dec. 6, 1955 2,831,898 Ecke et a1 Apr. 22, 1958 l l i l 

1. A LUBRICATING OIL SELECTED FROM THE GROUP CONSISTING OF PETROLEUM HYDROCARBN OILS AND SYNTHETIC DIESTER OILS NORMALLY SUSCEPTIBLE TO OXIDATIVE DETERIORATION CONTAINING A SMALL ANTIOXIDANT QUNATITY OF A SYNERGISTIC MIXTURE CONSISTING OF FROM ABOUT 0.001 TO ABOUT 0.2 PERCENT BY WEIGHT BASED ON THE OIL OF PHOSPHORUS AS A DIALKYL HYDROGEN PHOSPHITE IN WHICH THE ALKYL GROUPS EACH CONTAIN UP TO ABOUT 12 CARBON ATOMS AND FROM ABOUT 0.01 TO ABOUT 3 PERCENT BY WEIGHT BASED ON THE OIL OF AN ORTHO-ALKYL PHENOL HAVING THE FORMULA 